use glob instead of fs.readdirSync since /less now has subdirs
rename generateCustomCSS to generateCustomLess for accuracy
enhance customizer to handle transitive Less @import-s
grunt update-shrinkwrap build-customizer dist
Merge pull request #13047 from twbs/fix-customizer

Fix customizer (see #13043)
Customizer: switch to UglifyJS2 (v2.4.13).

The uglify build is generated with `uglifyjs --self -o uglify.min.js`.
Add the jquery check in customizer's output.
Add the license header in the non minified build too.
Run `grunt`.